142 THE CAMBRIAN. Ibuh..81. 



Formations III and IV were referred to the Cambrian system, and 

 the formations above IV to the Silurian and Devonian systems, etc. 



The term Cambrian was used provisionally to unite the first two fos- 

 sil-bearing formations. The upper portion of formation No. IV, or the 

 limestone member, was subsequently, in 1869, referred to the Knox 

 dolomite. 



This preliminary report was followed in 1869 by the volume on 

 " Geology of Tennessee," in which all the strata now referred to the 

 Cambrian are described in detail. 1 A map illustrating the geographic 

 distribution of the formations in the State, and a transverse section 

 from the North Carolina line west, showing the stratigraphic relations 

 of the formations, accompanies the volume. 



In speaking of the age of the metamorphic rocks of eastern Tennes- 

 see, which have been referred to by various authors as altered Silurian 

 rocks, Prof. Safford says : 



I have no reason for believing that this group within Tennessee includes the 

 metamorphosed beds of any formation of more recent date than the Ocoee conglom- 

 erate and slates. A portion of the beds are certainly referable to the Ocoee group; 

 the remainder, although conformable, may be older, and most likely are. * * 

 Iu the northern part of the State, at many points, the passage of the Ocoee beds into 

 gneiss is gradual and apparent. A considerable part, indeed, of our metamorphic 

 rocks can be, I think, thus referred to these beds. The question as to the greater ago 

 of other parts is not so easily settled, and must remain open for the present. I know 

 of no sufficient reason for referring any of these rocks to the Huronian or Laurentian 

 series of Canada. 2 



.It will thus be seen that the line of demarcation between the pre- 

 Cambrian rocks and the Cambrian rocks has not been closely defined 

 in Tennessee. It is only by comparison with the more clearly defined 

 line found in the sections of the Blue Eidge in Virginia that we are led 

 to consider that the metamorphosed rocks belong to an Algonkian 

 group between the Cambrian and the Archean. The studies which are 

 now in progress under the direction of the Geological Survey clearly 

 demonstrate this, and give as the base of the Cambrian a series of sand- 

 stones. Where the sandstones and conglomerates are made up of the 

 material derived from the adjacent Algonkian or Archean rocks they 

 will necessarily have something of the character of those rocks, and it 

 may be difficult in many instances to indicate the actual line of demarc- 

 ation, especially where the basal beds have been more or less altered 

 and disturbed by the subsequent folding, faulting, and compression 

 that accompanied the Appalachian uplift. 



As defined by Safford, Series II, or the Potsdam group of Tennessee, 

 consists of — 



1. The Ocoee conglomerate and slates. 



2. The Chilhowee sandstone. 



3. The Knox group of shales, dolomites, and limestones. 



'Geology of Tennessee. Nashville, 1869, pp. 182-226. a Op. cit, pp. 17!?, 178. 



